Electrostatic coating apparatus

ABSTRACT

Apparatus for electrostatically applying a coating of a substantially dry, solid particulate coating material to an article comprising an electrostatic spray head which is in communication with a source of the coating material. The spray head has particle-charging means which in a preferred form thereof includes a plurality of electrically conductive, spirally arranged, bristle-like extensions. Each of the extensions has its longitudinal axis positioned substantially transversely to the path of travel of the particles of the coating material, and has at least one free end for contacting and imparting an electric charge to the particles. A container for the coating material is in communication with the spray head through a material-supply conduit. Pressurized-air distribution means is provided in the container for maintaining the coating material in the container in a fluidized state. A Venturi, or injection, tube arrangement carried by the container acts to entrain the fluidized coating material. The container desirably is used in conjunction with a weight actuated device for automatically maintaining a sufficient supply of coating material in the container.

United States Patent 1 Witte 1 Jan. 16, 1973 [54] ELECTROSTATIC COATING APPARATUS Primary Examiner-Allen N. Knowles Assistant Examiner lohn J. Love [75] Inventor Bruce W Elmhurst Attrney-Wallenstein, Spangenberg, Hattis & Stram- [73] Assignees: Leo L. Glick, River Forest; Wallen- 'pel stein, Spangenberg, Hattis & Stram- V pel, Chicago, Ill. part interest to [57] ABSTRACT each -Apparatus for electrostatically applying a coating of a [22] Filed: Oct. 20, 1969 substantially dry, solid particulate coating material to an article com risin an electrostatic s ra head [2]] Appl' 867501 which is in comr iiunicition with a source 0% th e coating material. The spray head has particle-charging [52] 0.8. CI. .239/15, 222/195 means which in a preferred form thereof includes a [51] Int. Cl. ..Bb 5/02 plurality of electrically conductive. p y arranged, 5 Field of Search 239 3 15 437 33 4 9; bristle-like extensions. Each of the extensions has its 222/195; 317/3 longitudinal axis positioned substantially transversely to the path of travel of the particles of the coating 5 References m material, and has at least one free end for contacting and imparting an electric charge to the particles. A v UNITED STATES PATENTS container for the coating material is in communication 2 011 133 8/1935 Yoss ..222 195 with P l a materlal'supPly 2:070:972 2/1937 Lindenblad. .....239/15 x w 1 mm means the 2,657,339 /1953 Hampem mung/l5 X container for maintaining the coating material in the 2,792,262 5/l957 Hathomm 222/195 UX container in a fluidized state. A Venturi, or injection, 3 029 000 4 19 2 Kobee 222/195 tube arrangement carried by the container acts to en- 3,049,301 8/1962 Heuschkel... .....239/ train the fluidized coating material. The container 3,086,711 4/1963 Point ..239/ 15 desirably is used in conjunction with a weight actuated 3,134,513 5/1964 Ashman 222/195 X device for automatically maintaining a sufficient 3,212,2l l 10/1965 Bennett ..239/l5 of coating material in the container 3,327,948 6/1967 Gignoux ..239/15 X 3,498,540 3/1970 Adams ..239/15 21 Claims, 12 Drawing Figures 42 3 -l- 34 I0 5 52 t 56 58 k PATENTEDJANIS ms 3.711.022,

snmlura iiini FRO M A.C.

INVENTOR BRu-cs J. WITTE.

a n W,

M An s.

ELECTROSTATIC COATING APPARATUS This invention relates to apparatus for, and a method of, electrostatically coating articles with a substantially dry, solid particulate coating material.

Apparatus for electrostatically spraying articles with liquid paints has been thesubject matter of intensive development work over the years, and, as a result, has reached a comparatively advanced stage in the art. While many of the problems relating to electrostatic techniques for coating articles with liquid paints have been solved, the use of liquid points has certain signifi- .cant disadvantages, particularly from the standpoint of the high voltage inputs, usually 100,000 volts, or more, required adequately to charge the particles of the atomized paint and to establish an electrostatic field of suitable intensity and length, the amount ofliquid paint required to cover a given area, the unrecoverable paint losses due, in the main, to overspray, and the fire hazards due to the high flammability of the solvents used as bases for the paints. More recently, efforts directed toward overcoming the aforementioned, as well as other, disadvantages of using liquid paints in electrostatic coating operations, have led to the development of apparatus for electrostatically coating articles with solid coating materials. In operation, such apparatus involves flowing, as by pressurized-air, a stream of a substantially dry, solid particulate, heatmeltable or thermoplastic coating material through a spray head where the particles of the coating material are changed. In one form of apparatus of this type, a needle, connected to a source of high voltage and positioned at the nozzle of the spray head, is employed to impart a charge to the moving particles-The charged particles then pass through an electrostatic field of proper polarity, and suitable intensity and length, into contact with an article to be coated. The article is connected to a high voltage terminal of opposite polarityto that of the charge onthe particles, and may be preheated to effect melting of the coating material and the formation of a continuous film or coating thereon, or the article, with the charged particles thereon, may be passed through a heating station where melting and formation of a continuous film or coating takes place. Any particles which do not adhere to the article are recovered and re-used.

Despite the important advantages of solid particle over liquid paint spraying, solid particle spraying has not achieved any substantial commercial success due,

chiefly, to a number of significant shortcomings of the solid particle spray equipment heretofore developed. More specially in this latter connection, such equipment, like liquid paint electrostatic spray equipment, is characterized by the need for high voltage inputs, generally 100,000 volts, or-more, to adequately charge the particles of the coating material and to establish an electrostatic field of suitable intensity and length. In addition, films or coatings produced on an article with such equipment are, in most instances, extremely thin, usually I to 1.5 mils, and lack uniformity. Also, the equipment is incapable of uniformly covering irregular surfaces, and cannot very effectively be used to cover surfaces fabricated of non-conductive materials. A

further important disadvantage of the equipment resides in its overall cumbersomeness and bulkiness.

In accordance with the present invention, apparatus for electrostatically coating articles with dry, solid particulate coating materials is provided which not only is more compact and more economical, both from an operational and initial cost standpoint, than heretofore available apparatus of the type here under consideration, but which also enables a more extensive and more uniform coating over a wide range of thicknesses to be attained on articles of simple or highly irregular configuration than is possible with heretofore available solid particle spray'ing equipment. More specifically, the apparatus of this invention can provide uniform coatings, ranging upwards of mils in thickness on articles, utilizing energy inputs of the order of about 25,000 to about 50,000 volts. These results, furthermore, can be attained on articles fabricated of a nonconductive material like glass, and in the case of articles of smaller size, coatings of the type indicated can be provided on all sides of the article without the need for revolving the article. Solid particulate coating materials of the polymeric or the porcelain type can be used with equal facility in the apparatus. The apparatus, in addition, is easily and readily portable by one man, and lends itself to manual as well as automated article coating operation.

The apparatus of this invention, in part, comprises a spray head which is associated with conduit means for delivering a stream of a solid particulate coating material to the spray head from a source thereof. The spray head, at its outlet or nozzle, is provided with particle charging means for imparting an electric charge to the particles of the coating material. The particle charging means includes a plurality of electrically conductive, radially arranged, longitudinally spaced extensions, each of which has its longitudinal axis positioned substantially transversely to the path of travel of the stream of coating material, and has at least one free end for contacting and imparting an electric charge to the particles of the coating material. In a preferred embodiment of the spray head of this invention, the particle charging means is in the form ofa short, wire brush, the bristles of which are spirally arranged on the heavy gauge wire core or axis thereof, and are progressively shortened in the direction of the nozzle of the spray head thereby to provide a tapered configuration to the brush This arrangement enables the particles of the coating material to make contact with, and be charged by, more than one of the particle charging extensions or bristles. The substantially completely charged particles thus produced can more effectively move through the electrostatic field established near the article to be coated, and can make better contact with, and provide a uniform coating, over a wide range of thicknesses, on the article. Apart from the more complete charge imparted to the particles by the extensions or bristles, the spiral arrangement thereof serves to provide greatly enhanced dispersion of the coating material and sets up a swirling action in the stream of charged particles which persists as the particles transverse the electrostatic field and come into contact with the article to be coated. The swirling action provides for more effective, fuller and more uniform distribution of the charged particles on the article, even to the extent of enabling them, in the case of articles of smaller size, to envelop and uniformly coat all sides thereof.

In accordance with another aspect of the present invention, the dry, solid particulate coating material is conveyed to the spray head from a container, which, apart from its compactness, incorporates features which constitute an important part of the invention. In

' its preferred form, the container has a Venturi, or inconduit, which, in cooperating with motor-driven agitator means, acts to maintain a substantial quantity of the coating material in a fluidized state. The remaining portion of the pressurized air is directed into the Venturi, or injection, tube, and serves to entrain the fluidized coating material and to carry it to the spray head. Flow of pressurized air to the container, and energization of the motor for driving the agitator, as well as energization of the high energy source, conveniently are controlled at the spray head.

In accordance with still another aspect of the invention, a weight-actuated device is provided for the coating material supply container for automatically maintaining an adequate supply of dry, solid particulate material in the container during operation of the spray head. As an added feature, the weight-actuated device has switch controlled vibrating means which acts to dislodge residual coating material from the container when it is desired to substitute one coating material for another thereby to avoid contamination of coating materials.

These, and other advantages and features of the present invention will become apparent upon making reference to the specification to follow, the claims, and the drawings wherein:

FIG. 1 is a view in perspective of an embodiment of the apparatus of this invention illustrating its use in a typical electrostatic coating operation;

FIG. 2 is a side view in elevation, partly in section, of an embodiment of the spray head of this invention;

FIG. 3 is an enlarged vertical sectional view taken substantially along line 33 of FIG. 2;

FIG. 4 is a vertical sectional view of an embodiment of the coating material supply container of the present invention;

FIG. 5 is a fragmentary side view in elevation, partly in section, of the top of said embodiment of the container;

FIG. 6 is a horizontal sectional view taken substantially along line 6-6 of FIG. 4;

FIG. 7 is a horizontal sectional view taken substantially along line 7-7 of FIG. 4;

FIG. 8 is a circuit diagram illustrative of the operating electrical circuits for spray head shown;

FIG. 9 is a fragmentary vertical sectional view taken substantially along line 9-9 of FIG. 1;

FIG. 10 is a top plan view of an embodiment of the weight-actuated container refilling device of this invention;

FIG. 11 is a fragmentary front elevational view of said embodiment of the refilling device; and

FIG. 12 is a circuit diagram illustrative of the operating electrical circuits for said embodiment of the refilling device.

Referring, now, in particular to FIG. 1 of the drawing, the embodiment of the apparatus there shown being used in an electrostatic coating operation comprise's a spray head 10, a coating material supply container l2, and a weight-actuated, automatic coating material refilling unit 14. A coating material supply conduit 16 is connected to the spray head 10 and the container 12. Charging of the particles of the coating material, and establishment of an electrostatic field between the spray head 10 and an article 18 being carried on a grounded conveyor 20, for example, is attained by connecting the spray head 10 and the article 18 to a suitable high voltage source 22. Illustrative circuit diagrams of the operating electrical circuits for the apparatus, as shown, are the subject matter of FIGS. 8

, and 12, and will be described in detail hereinafter.

As shown in FIGS. 2 and 3 of the drawing, the embodiment of the spray head 10 shown has a pistol-like configuration, and comprises a barrel portion 10a and a pistol-grip or handle portion 10b. The barrel portion 101: and the handle portil0b are held in position with relation'to one another by a connector member 10c. The barrel 10a has a nozzle 30 secured to the forward end 32 thereof. As illustrated, the nozzle 30 is retained in position by a collar 34 having internal threads 36 for engaging external threads 38 on the end 32 of the barrel portion 10a. The front wall 42 of the collar 34 engages an annular extension 44 on the nozzle 30 to hold the nozzle firmly against the muzzle of the barrel por tion 10a when the threads 36 and 38 are tightly engaged. The barrel portion 10a the handle portion 10b the nozzle 30 desirably are fabricated of a non-conductive, impact-resistant material such as plastic. While fabricated spray head 10, as shown, is comprised of a number of separable elements, it should be understood, of course, that the spray head may be formed as an essentially unitary, one-piece structure.

The barrel portion 10a has a coating material channel or passageway 50 which communicates at one end with an open-ended chamber 52 in the nozzle 30 and at its other end with the coating material supply conduit 16. The inner wall of the nozzle 30 is chamfered as at 54 to provide the chamber 52 with an outwardly flared outlet 56. A metal sleeve 58 is positioned in the passageway 50 and extends partly into the chamber 52 of the nozzle 30. Positioned in the metal sleeve 58, and also extending partly into the chamber 52, is a particle ionizing or charging body 60. The body 60, in the embodiment illustrated, advantageously comprises a wire brush having a plurality of short, spirally arranged metal bristles 62 which are anchored in a pair of elongated, spirally wound heavy gauge wires 6464. The bristles 62, at the forward end 66 of the brush, are gradually shortened to provide a tapered configuration to the brush. By thus tapering the brush, and extending the forward end 66 thereof beyond the outlet end of the sleeve 58 and into the restricted chamber 52 of the nozzle 30, the particles of coating material are able to make contact with a multiplicity of the bristles 62 as the particles move from the sleeve 58.into the chamber 52. As a result, substantiallyall facets or sides of the particles are charged. The spiral arrangement of the bristles 62 acts to filter and swirl the particles of coating material as they make contact with the bristles thereby providing enhanced dispersion of the coating material. The body 60 is charged by a cable 70, which is connected to the power supply 22 through means provided on the container 12. A narrow passageway 72 is formed in the barrel portion a to receive the cable 70. A bare end 74 of the cable 70 is in contact with the sleeve 58 which supports the body 60. The end 74 of the cable 70, of course, can, if desired, be placed in direct contact with the body 60. The handle portion 10b of the spray head 10 has a finger actuated switch 80. A pair of leads 82 and 84 are connected to the switch 80 for energizing, among other things, the body 60.

Referring, now, to FIGS. 4 through 7, the coating material supply container 12 from which a stream of coating material is caused to flow to the spray head 10 comprises a body portion 90 having an open top 92. A lid 94, and screw-operated lid clamp 96 are provided for the body portion 90. The portion 90 has an openbottomed base 98 which serves both as a support for the container and a housing for various functional components associated with the container 12. The coating material 100 in the body portion 90 of the container may be any of various commercially available plastic or porcelain powders or a floccing material such as wool, cotton, nylon fibers, or the like. The particle size of the coating material should, of course, be such that clogging of the apparatus will not occur. In the case of plastic powders, for example, the particle size advantageously should range from about 100 to 350 mesh. Typical of plastic powders having utility in connection with the apparatus of this invention are the polyester and epoxy powders sold under the trademarks CORVEL and Blue Epoxy LC 1432 (The Polymer Corporation). CORVEL has a bulk density, at rest, of 65 lbs/ft. and a fusion temperature of 275 F, while the epoxy powder has a bulk density, at rest, of 37.6 lbs/ft. and a fusion temperature of 350 F.

Fluidization of the coating material 100 in the body portion 90 of the container 12 is attained by positioning a pressurized air or turbulence conduit 102 in the portion 90. The turbulence conduit 102 desirably has a spiral-like shape and is adapted to be received in a channel or recess 104 formed in the bottom wall 106 of the portion 90. One end 108 of the turbulence conduit 102 is sealed. The other end 110 is connected to a bypass conduit 112 which is in communication with a pressurized-air conduit 114 through a coupling 116. The pressurized-air conduit 114, in turn, is connected to an air solenoid 118 to which air under pressure is supplied from a source, not shown. In the embodiment illustrated, the turbulence conduit 102 has a plurality of spaced, inwardly directed holes or opening 120. As illustrated by the arrows in FIG. 4, the holes or openings 120 desirably are formed in the conduit 102 at an angle of from about to with respect to normal. The curvature of the turbulence conduit 102, and the angle of the holes or openings 120 formed therein, enable the pressurized air passing into the body portion 90 through the holes or openings 120 to impart a swirling or circular movement to the particles of the coating material 100.

An elongated, downwardly extending fluidized coating material receiving chamber 122, having an enlarged, cup-shaped mount 124, is joined to the bottom wall 106 of the body portion 90. A narrow, angularly disposed conduit 126 connects the receiving chamber 122 with a Venturi, or injection, tube 130 positioned downstream from the by-pass conduit 112 and the coupling 1 16. The Venturi, or injection, tube communicates with the pressurized air conduit 114 through the coupling 116, and is joined to the coupling 116 by an inlet conduit 132. The inlet conduit 132 is joined at its outlet end to an air injection conduit 134 of small diameter. The outlet end of the conduit 134 is positioned adjacent the outlet 136 of the conduit 126. Downstream of the outlet end of the air injection conduit 134, a restricted passageway 138 is provided in the Venturi, or injection, tube 130. A nipple 140 is connected to the outlet end of the tube 130. The outlet end of the nipple 140, in turn, is connected to the coating material supply conduit 16.

In order to prevent any lumpy, or agglomerated coating material from entering the Venturi, or injection, tube 130 through the chamber 122 and the conduit 126 an agitator 142 is positioned above the mouth 124 of the chamber 122. A toothed wheel 144, which functions as a metering device for the fluidized coating material, is positioned within the mouth 124 of the chamber 122. The agitator 142 and the wheel 144 are secured on a shaft 146 which is driven by a motor 150.

The container 12 carries an actuating relay 152 which is connected to the switch 80 of the spray head 10 through leads 82 and 84. As shown in FIG. 1, the relay 152 also is connected to the high energy power source 22 through a cable 154, and to an A.C. power source through a cord 156. As best shown in FIG. 5, the

body portion 90 of the container 12 is provided with a pressure relief valve 160, an inert gas inlet 162, a coating material supply connector 164, and a pressure gauge 166, the purpose of each of which will become clear as the description proceeds.

Referring, now, to FIGS. 9 and 10 of the drawing, the embodiment of the weight-actuated coating material refilling unit 14 comprises an open-bottomed housing to the upper wall 172 of which are secured a plurality of compression or torsion springs 174. Pins 176 are secured to the wall 172 and extend though the springs 174. The pins 176 are received in openings 178 formed in the bottom wall of the base portion 98 of the container 12, and thus serve to prevent the container from being dislodged from its position on the unit 14. A movable lever or sensing arm 180 extends through a slot 182 in the upper wall 172. The free end of the arm 180 is adapted to engage the base portion 98 of the container 12. The other end of the arm 180 acts to open and close the contacts of micro-switches 184- 184. A powder supply solenoid 186, connected to the micro-switches 184184, is provided for automatically controlling flow of coating material from a source thereof (not shown) to the container 12 through a'conduit 164a attached to the connector 164 (see FIG. 1). An unloading solenoid 190, connected to the base'portion 98 of the container 12 by a slotted arm 192, and actuated by a manual switch 194, is secured to the bottom wall of the housing 170. The unloading solenoid has an armature provided with a head portion 190a and a neck portion 19%. The head portion 190a is normally biased against one end of the slotted arm 192 by a spring 1900. The portions 190a, 190b, and the arm 192, upon energization of the coil of the solenoid 190, move rapidly up and down thereby causing the container 12 to vibrate. To compensate for differences in the bulk density of coating materials used in connection with the apparatus, an override spring 196 is secured to the upper wall 172 of the housing 170. A metal strap or bar 198 hinged at one of its ends 198a, is in contact with the base of the spring 196. The tension on the spring 196 is controlled by changing the angle of the strap or bar 198 with relation to the spring 196. This is conveniently accomplished by means of a control handle 200 which can be manually moved to the right or left in a horizontal slot 202 formed in the end wall 204 of the housing 170. A signal light 206 is provided to indicate that coating material is flowing from the container 12. A light cord 208 serves to connect the unit 14 to a conventional l 10 volt A.C. outlet. Index or scale means 210 is conveniently provided on the end wall 204 above the slot 202 to facilitate proper setting of the handle 200 for coating materials of different bulk densities.

Operation of the apparatus is initiated by depressing the switch 80 on the handle 10b of the spray head 10 to energize the activating relay 152 carried by the container 12. Energization of the relay 152 acts to close contacts within the relay thereby energizing the motor 150 and the air solenoid 118, and causing power to be supplied to the spray head 10 by the high energy supply source 22. Upon energization of the solenoid 118, air flows into the turbulence tube 102 causing the powder 100 therein to be swirled and fluidized in the container 12. Simultaneously, air is passed into the Venturi, or injection, tube 130. An area of reduced pressure is created in the tube 130, causing the fluidized powder to be entrained in the air stream. Assuming, for purposes of illustration, thatair at a pressure of 30 psig is passing through the conduit 114. The portion thereof which is diverted to the turbulence tube 130 will enter the body portion 90 of the container 12 at a pressure of approximately 22 psig. The pressure of the air passing out of the Venturi, or injection, tube 130, will have a pressure of approximately 8 psig. The agitator 142 acts to maintain powder in a fluidized state as it is drawn into the chamber 122, while the toothed wheel 144, as stated, serves as a metering device to control the amount of fluidized powder passing into the chamber 122 from the body portion 90 of the container 12.

The air-entrained powder is carried to the spray head 10 through the supply conduit 16. It then passes through the passageway 50 and into the sleeve 58. The moment the powder makes contact with the sleeves 58, the particles thereof begin to take on an electrical charge. As the particles come into contact with the extensions 62 of the particle charging body 60 they become fully charged. As indicated, this result is achieved by causing the particles to come into contact with a multiplicity of the extensions which 'are' gradually shortened in the direction of travel of the particles. Each of the extensions is a discharge emitter, and the spiral arrangement thereof acts both to slow up the particles as they make contact with the extensions, and

to impart a swirling action to the particles which more I effectively disperses them and enables each facet thereof to receive a charge. The charged particles then pass through the nozzle of the spray head and through the electrostatic field established between the spray head and an article to be sprayed. Upon making contact with the article, which has a polarity or charge opposite to that of the charged particles, the particles adhere thereto. The swirling action imparted to the particles by the spirally arranged extensions 62 is maintained as the particles pass through the electrostatic field, and greatly enhances the uniformity of dispersion of the charged particles on the article. As shown in FIG. 1, the articles 18 may be preheated, or they may be passed, after spraying, through an oven or heating unit 220 where the particles are melted or fused to form a uniform, smooth coating or film on the articles.

To effect the automatic control described hereinabove, reference is made to the illustrative wiring diagram shown in FIG. 8. The switch 80, on the spray head 10, has a movable contact a, and a pair of stationary contacts 80b and 800. The contacts, as illustrated, are in a normally open position. The-stationary contact 80b is connected through lead 82 to A.C. power supply line 230. The other stationary contact 800 is connected through lead 84 to the relay 152. The relay 152 is provided with three sets of normally open contacts 152a, 152b, and l52c connected,respectively, to the motor 150, the air solenoid 118 and to the high energy source 22. One terminal of the primary coil 232 of the high energy source 22 is connected to the A.C. power supply line 234. When the contacts of the switch 80 are closed, the coil of the relay 152 is energized and the contact 152a, 152b and 1520 are closed, thereby energizing the motor 150, the air solenoid 118 and the high energy source 22. Upon releasing the switch 80, the relay 152 is de-energized,and the contacts 152a, l52b and 1526 are opened.

Referring, now, in particular to FIGS. 912, in utilizing the automatic refilling unit 14, the container 12 is first positioned on the springs 174. As stated hereinabove, the unit 14 is a weight actuated device, and the springs 174 are tensioned to suspend the container 12. Assuming the container 12 is empty, or nearly so, the arm will act to close the contacts of the micro-switches 184l84. The powder supply solenoid 186 will thereupon become energized, and powder will start to flow from a source (not shown) through the conduit 164a attached to the connector 164 on the container 12. As the body portion of the container 12 fills with the powder, the combined weight of the powder and the container overcomes the tension of the springs 174, and the arm 180 is depressed, opening the contacts of the micro-switches 184184, and de-energizing the solenoid 186. In order to maintain a continuous, smooth, even flow of powder during the refilling operation, a mechanical time delay arrangement is provided for the micro-switches 184 184. This is achieved by arranging the switches in series and making the pusher bar (not shown) on one of the switches longer than that of the other switch. During the refilling operation, the indicator light 206 remains on. The override-spring 196 acts to compensate for powders or coating materials of different bulk density which may be used in the apparatus. The base of the spring 196 is in continuous contact with the inclined, pivotally mounted bar 198. The bar 198 rests on the handle 200 which, as indicated hereinabove, can be moved to vary the tension on the spring 196 in accordance with the bulk density of the powder or other coating material in the container 12. The unit 14 also can be used to empty the container 12 of unused coating material. To this end, the manual switch 194 is depressed thereby energizing the unloading solenoid 1510. The solenoid 190, which is connected to the bottom of body portion 90 of the container 12 through the slotted arm 192, acts to shake or vibrate the container 12 causing any coating material therein to fall into a trough (not shown) in the bottom of the body portion 90. The trough can be emptied by removal of a plug (also not shown) provided in the bottom wall 106 of the body portion 90. I

FIG. 12 illustrates a wiring diagram for effecting operation of the unit 14 as described hereinabove. As shown, the manual switch 194 comprises two pairs of stationary contacts 240240 and 242242 and two movable contacts 244 and 246. One of the stationary contacts 240 is connected to an A.C. power supply line 250, while the other contact 240 is connected to the indicator light' 206. Both during operation of the spray head and refilling of the container 12, the movable contact 244 and the stationary contacts 240-240 are engaged, as shown. The micro-switches 184-184 each comprises a movable contact 184a and a stationary contact 184b. The stationary contact 184k of one of the switches 184 is connected to AC. power supply line 252. The stationary contact 184b of the other microswitch is connected to the powder supply solenoid 186. The micro-switches l84184 are shown in an open position, in which position they remain until the container 12 requires more powder. When the contacts of the micro-switches are closed, the powder supply solenoid 186 is energized, and powder flows to the container through the conduit 164a until the tension of the springs 174 is overcome and the arm 180 is depressed to open the contacts of the micro-switches. When it is desired to empty the container 12 of any residual powder in the body portion 90 thereof, the manual switch 194 is depressed, opening contacts 240-240 and closing contact 242242. The unloading solenoid 190 is thus energized causing the spring suspended container 12 to be shaken or vibrated.

During the operation of the apparatus, nitrogen, or other inert gas, advantageously is injected into the container 12 through the inlet 162 to reduce the possibility of explosion. The pressure relief valve 160 acts to relieve any excess pressure developed in the container 12 resulting from fluidization of the coating material. The pressure gauge 166 enables an operator to determine at all times the pressure condition in the container 12.

While the present invention has been shown and described with relation to certain specific embodiments thereof, it should be understood that those embodiments are capable of many modifications. Changes, therefore, in the construction, arrangement, or manner of carrying out the invention may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. An electrostatic spray head for electrostatically coating the surface of an article with a solid particulate coating material, comprising conduit means for receiving a stream of coating material particles from a source thereof, particle charging means at the end of said conduit means where the coating material particles leave the spray head for imparting an electric charge to the particles of the coating material, said particle charging means including a plurality of electrically conductive,

longitudinally spaced wire-like extensions distributed over the area to be occupied by the stream of coating material particles leaving the spray head, each of said wire-like extensions positioned substantially transversely to the path of travel of the stream of coating material particles and at least some of the transversely extending longitudinally spaced wire-like extensions having free ends for contacting and imparting an electric charge to the particles of the coating material, and means for coupling a source of high voltage to the wirelike extensions.

2. An electrostatic spray head according to claim 1 wherein the charge-imparting wire-like extensions extend transversely to the path of travel of said particle stream in many different radial directions.

3. An electrostatic spray head according to claim 1 wherein the free ends of the charge-imparting extensions are located at progressively different radial positions in the direction of travel of the coating material particles.

4. An electrostatic spray head according to claim 1 wherein the wire-like extensions are anchored on a common support member and are spirally arranged thereon.

5. An electrostatic spray head according to claim 1 wherein the particle charging means comprises a wire brush, the wire bristles of which are secured to a common support member and are spirally arranged thereon.

6. An electrostatic spray head according to claim 5 wherein the bristles are gradually diminished in length to impart a tapered configuration to the brush.

7. An electrostatic spray head according to claim 1 wherein the conduit means includes a conductive sleeve with which a portion at least of the extensions are in contact.

8. An electrostatic spray head according to claim 1 wherein the conduit means includes a chamber in which a portion at least of the extensions are positioned, the free ends of said portion of the extensions being spaced from the side walls of the chamber.

9. An electrostatic spray head for electrostatically coating the surface of an article with a solid particulate coating material, comprising a body portion, conduit means in the body portion connected to a source of coating material particles, particle charging means positioned in the conduit means for imparting an electric charge to the particles of the coating material, said particle charging means including a plurality of electrically conductive, longitudinally spaced, charge-imparting wire-like members extending in a direction across the conduit in many different radial directions so as to be positioned substantially transversely to the path of travel of the particles of the coating material through the conduit means and distributed substantially over the area to be occupied by the stream of coating material particles leaving the spray head, and means for connecting a source of high voltage to the particle charging means.

10. A spray head according to claim 9 wherein the particle charging means comprises a wire brush, the wire bristles of which are secured to a common support member and are spirally arranged thereon.

11. A spray head according to claim 9 wherein the body portion has a nozzle end which defines a chamber in which a portion at least of said extensions are positioned.

12. A spray head according to claim 9 wherein the body portion is provided with a passageway for receiving conductor means for connecting the particle charging means with a source of high voltage.

13. A spray head according to claim 9 wherein the handle of the spray head has switch means for controlling the energization and de-energization of the particle charging means.

14. Apparatus for electrostatically coating an article with a solid particulate material, said apparatus comprising: a container for holding a supply of substantially dry, solid coating material particles and including an outlet at the bottom of said container; a source of pressurized. gas; a conduit for carrying the coating material particles from said container to a spraying head; particle entraining means connected between said source of pressurized gas, the inlet end of said conduit and said outlet for withdrawing said coating material particles from said container and for entraining the same in the moving gas from said source of pressurized gas directed to the inlet end of said conduit; means for fluidizing the material in said container before being entrained in the gas; means for directing a number of upwardly directed streams of high pressure gas in the bottom of said container around said outlet; agitator means in said container at the point where the coating material particles leave the bottom of the container for beating and breaking up'agglomerated particles-thereat; metering means in the path of movement of coating material particles leaving the bottom of the container for providing a limited clearance space for the passage of coating material particles from said container; an electrostatic spray head connected to the outlet end of said conduit, said spray head having a passageway between the inlet and outlet ends thereof head particle charging means at the outlet end of said passageway where the coating material particles leave the spray head for imparting an electrical charge thereto, said particle charging means including a plurality of electrically conductive wire-like members distributed substantially over the area to be occupied by the stream of coating material particles leaving the spray head, said wire-like members extending substantially transversely to the path of travel of the stream of coating material particles, at least some of said wire-like members having free ends for contacting and imparting an electric charge to the particles of the coating material; means for coupling a source of high voltage to said wire-like members having free ends; valve means for selectively coupling and uncoupling said source of pressurizedgas to and from said conduit and particle entraining means; and a manually operable control member for operating said valve means quickly to start and stop the movement of fluidized particles between said container and said conduit extending to said spray head.

15. An electrostatic spray head for electrostatically coating the surface of an article with a solid particulate coating material, comprising conduit means for receiving streams of coating material particles entrained in a moving body of gas, particle charging means at the end of said conduit means where the coatin material particles leave the spray head for impar ing an electrlc charge thereto, said particle charging means including a plurality of electrically conductive, closely laterally spaced, wire-like members distributed substantially over the area to be occupied by the stream of coating material particles leaving the spray head, said wire-like members extending substantially transversely to the path of travel of the stream of coating material particles at least some of said transversely extending wire-like members having free ends for contacting and imparting an electric charge to the particles of the coating material, and means for coupling a source of high voltage to said wire-like members having free ends.

16. The electrostatic spray head of claim 15 wherein said particle charging means includes longitudinally as well as laterally charge-imparting wire-like members extending in a direction across the stream of coating material particles and projecting radially in various directions, the ends of both longitudinally and laterally spaced wire-like members having free ends to impart charge to said particles.

17. The electrostatic spray head of claim 15 wherein the free ends of the charge-imparting wire-like members are located at different radial positions in the stream of moving coating material particles leaving the spray head.

18. The electrostatic spray head of claim 15 wherein said wire-like members project outwardly from a central support member and are spirally arranged thereon so the wire-like members act to displace and swirl the particles.

19. The electrostatic spray head of claim 1 wherein the projection of said longitudinally spaced extensions on a plane transverse to the direction of movement of said particles of coating material will form closely spaced lines distributed over the entire area thereof.

20. An electrostatic spray head for electrostatically coating the surface of an article with a solid particulate coating material, comprising conduit means for delivering a stream of particulate coating material to the spray head from a source thereof, particle charging means in the spray head for imparting an electric charge to the particles of the coating material, said particle charging means comprising a wire brush, the wire bristles of which are secured to a common support member and spirally arranged thereon to form a plurality of electrically conductive, longitudinally spaced extensions, each of said extensions having its longitudinal axis positioned substantially transversely to the path of travel of the stream of coating material and having at least one free end for contacting and imparting an electric charge to the particles of the coating material; and means for coupling a source of high voltage to the particle charging means.

21. An electrostatic spray head according to claim 20 wherein the bristles are gradually diminishedin length to impart a tapered configuration to the brush. 

1. An electrostatic spray head for electrostatically coating the surface of an article with a solid particulate coating material, comprising conduit means for receiving a stream of coating material particles from a source thereof, particle charging means at the end of said conduit means where the coating material particles leave the spray head for imparting an electric charge to the particles of the coating material, said particle charging means including a plurality of electrically conductive, longitudinally spaced wire-like extensions distributed over the area to be occupied by the stream of coating material particles leaving the spray head, each of said wire-like extensions positioned substantially transversely to the path of travel of the stream of coating material particles and at least some of the transversely extending longitudinally spaced wire-like extensions having free ends for contacting and imparting an electric charge to the particles of the coating material, and means for coupling a source of high voltage to the wire-like extensions.
 2. An electrostatic spray head according to claim 1 wherein the charge-imparting wire-like extensions extend transversely to the path of travel of said particle stream in many different radial directions.
 3. An electrostatic spray head according to claim 1 wherein the free ends of the charge-imparting extensions are located at progressively different radial positions in the direction of travel of the coating material particles.
 4. An electrostatic spray head according to claim 1 wherein the wire-like extensions are anchored on a common support member and are spirally arranged thereon.
 5. An electrostatic spray head according to claim 1 wherein the particle charging means comprises a wire brush, the wire bristles of which are secured to a common support member and are spirally arranged thereon.
 6. An electrostatic spray head according to claim 5 wherein the bristles are gradually diminished in length to impart a tapered configuration to the brush.
 7. An electrostatic spray head according to claim 1 wherein the conduit means includes a conductive sleeve with which a portion at least of the extensions are in contact.
 8. An electrostatic spray head according to claim 1 wherein the conduit means includes a chamber in which a portion at least of the extensions are positioned, the free ends of said portion of the extensions being spaced from the side walls of the chamber.
 9. An electrostatic spray head for electrostatically coating the surface of an article with a solid particulate coating material, comprising a body portion, conduit means in the body portion connected to a source of coating material particles, particle charging means positioned in the conduit means for imparting an electric charge to the particles of the coating material, said particle charging means including a plurality of electrically conductive, longitudinally spaced, charge-imparting wire-like members extending in a direction across the conduit in many different radial directions so as to be positioned substantially transversely to the path of travel of the particles of the coating material through the conduit means and distributed substantially over the area to be occupied by the stream of coating material particles leaving the spray head, and means for connecting a source of high voltage to the particle charging means.
 10. A spray head according to claim 9 wherein the particle charging means comprises a wire brush, the wire bristles of which are secured to a common support member and are spirally arranged thereon.
 11. A spray head according to claim 9 wherein the body portion has a nozzle end which defines a chamber in which a portion at least of said extensions are positioned.
 12. A spray head according to claim 9 wherein the body portion is provided with a passageway for receiving conductor means for connecting the particle charging means with a source of high voltage.
 13. A spray head according to claim 9 wherein the handle of the spray head has switch means for controlling the energization and de-energization of the particle charging means.
 14. Apparatus for electrostatically coating an article with a solid particulate material, said apparatus comprising: a container for holding a supply of substantially dry, solid coating material particles and including an outlet at the bottom of said container; a source of pressurized gas; a conduit for carrying the coating material particles from said container to a spraying head; particle entraining means connected between said source of pressurized gas, the inlet end of said conduit and said outlet for withdrawing said coating material particles from said container and for entraining the same in the moving gas from said source of pressurized gas directed to the inlet end of said conduit; means for fluidizing the material in said container before being entrained in the gas; means for directing a number of upwardly directed streams of high pressure gas in the bottom of said container around said outlet; agitator means in said container at the point where the coating material particles leave the bottom of the container for beating and breaking up agglomerated particles thereat; metering means in the path of movement of coating material particles leaving the bottom of the container for providing a limited clearance space for the passage of coating material particles from said container; an electrostatic spray head connected to the outlet end of said conduit, said spray head having a passageway between the inlet and outlet ends thereof head particle charging means at the outlet end of said passageway where the coating material particles leave the spray head for imparting an electrical charge thereto, said particle charging means including a plurality of electrically conductive wire-like members distributed substantially over the area to be occupied by the stream of coating material particles leaving the spray head, said wire-like members extending substantially transversely to the path of travel of the stream of coating material particles, at least some of said wire-like members having free ends for contacting and imparting an electric charge to the particles of the coating material; means for coupling a source of high voltage to said wire-like members having free ends; valve means for selectively coupling and uncoupling said source of pressurized gas to and from said conduit and particle entraining means; and a manually operable control member for operating said valve means quickly to start and stop the movement of fluidized particles between said container and said conduit extending to said spray head.
 15. An electrostatic spray head for electrostatically coating the surface of an article with a solid particulate coating material, comprising conduit means for receiving streams of coating material particles entrained in a moving body of gas, particle charging means at the end of said conduit means where the coating material particles leave the spray head for imparting an electric charge thereto, saiD particle charging means including a plurality of electrically conductive, closely laterally spaced, wire-like members distributed substantially over the area to be occupied by the stream of coating material particles leaving the spray head, said wire-like members extending substantially transversely to the path of travel of the stream of coating material particles at least some of said transversely extending wire-like members having free ends for contacting and imparting an electric charge to the particles of the coating material, and means for coupling a source of high voltage to said wire-like members having free ends.
 16. The electrostatic spray head of claim 15 wherein said particle charging means includes longitudinally as well as laterally charge-imparting wire-like members extending in a direction across the stream of coating material particles and projecting radially in various directions, the ends of both longitudinally and laterally spaced wire-like members having free ends to impart charge to said particles.
 17. The electrostatic spray head of claim 15 wherein the free ends of the charge-imparting wire-like members are located at different radial positions in the stream of moving coating material particles leaving the spray head.
 18. The electrostatic spray head of claim 15 wherein said wire-like members project outwardly from a central support member and are spirally arranged thereon so the wire-like members act to displace and swirl the particles.
 19. The electrostatic spray head of claim 1 wherein the projection of said longitudinally spaced extensions on a plane transverse to the direction of movement of said particles of coating material will form closely spaced lines distributed over the entire area thereof.
 20. An electrostatic spray head for electrostatically coating the surface of an article with a solid particulate coating material, comprising conduit means for delivering a stream of particulate coating material to the spray head from a source thereof, particle charging means in the spray head for imparting an electric charge to the particles of the coating material, said particle charging means comprising a wire brush, the wire bristles of which are secured to a common support member and spirally arranged thereon to form a plurality of electrically conductive, longitudinally spaced extensions, each of said extensions having its longitudinal axis positioned substantially transversely to the path of travel of the stream of coating material and having at least one free end for contacting and imparting an electric charge to the particles of the coating material; and means for coupling a source of high voltage to the particle charging means.
 21. An electrostatic spray head according to claim 20 wherein the bristles are gradually diminished in length to impart a tapered configuration to the brush. 